Boundary forces

Boundary forces

This is an example of cs_user_extra_operations which computes boundary forces

Example 1: compute total forces on a boundary zone (subset of boundary faces).

  {
    const cs_lnum_t n_b_faces = domain->mesh->n_b_faces;

    cs_field_t *b_forces = cs_field_by_name_try("boundary_forces");

    if (b_forces != NULL) {
      cs_real_3_t total_b_forces = {0., 0., 0.};
      cs_lnum_t n_elts, *lst_elts;
      BFT_MALLOC(lst_elts, n_b_faces, cs_lnum_t);
      cs_selector_get_b_face_list("2 or 3", &n_elts, lst_elts);

      for (cs_lnum_t i_elt = 0; i_elt < n_elts; i_elt++) {
        cs_lnum_t face_id = lst_elts[i_elt];
        for (int ii = 0; ii < 3; ii++)
          total_b_forces[ii] += b_forces->val[3*face_id + ii];
      }
      BFT_FREE(lst_elts);

      /* parallel sum */
      cs_parall_sum(3, CS_DOUBLE, total_b_forces);
    }
  }

Example 2: compute pressure forces on a boundary zone (subset of boundary faces).

  {
    const cs_lnum_t n_b_faces = domain->mesh->n_b_faces;
    const cs_real_t *b_f_face_normal =
      domain->mesh_quantities->b_f_face_normal;

    cs_real_3_t total_b_p_forces = {0., 0., 0.};
    cs_lnum_t n_elts, *lst_elts;
    BFT_MALLOC(lst_elts, n_b_faces, cs_lnum_t);
    cs_selector_get_b_face_list("2 or 3", &n_elts, lst_elts);

    /* compute static pressure on selected boundary faces */
    cs_real_t *p_b_val;
    BFT_MALLOC(p_b_val, n_elts, cs_real_t);
    cs_post_b_pressure(n_elts, lst_elts, p_b_val);

    for (cs_lnum_t i_elt = 0; i_elt < n_elts; i_elt++) {
      cs_lnum_t face_id = lst_elts[i_elt];
      for (int ii = 0; ii < 3; ii++)
        total_b_p_forces[ii] += p_b_val[i_elt]*b_f_face_normal[3*face_id+ii];
    }
    BFT_FREE(lst_elts);
    BFT_FREE(p_b_val);

    /* parallel sum */
    cs_parall_sum(3, CS_DOUBLE, total_b_p_forces);
  }